Creosote has been in use for over three hundred years, U.K. patent No. 214 being issued to Becker, J. and Serle, H. in 1681. Its primary utilization has been in wood and fabric preservation with excursions into the fields of medicine, pharmacy, dyes, chemicals, carbon blacks and fuels.
The diverse and colourful history of creosote preservatives utilization and benefits has been marred only by inherent problems of odour, skin irritation and related product handling problems.
Drawbacks evidenced in the use of creosote in recent times are those of heating costs in plant use, flammability, odour, pollution and unacceptable oily, tarry or crud coated deposits on the surfaces of treated wood. Some or all of the above limit the use of creosote to the treatment of timber which is unlikely to come into contact with people or livestock. The inherent properties of raw creosote preclude its use in domestic applications and building or fabrication timbers in which an aesthetically pleasing wood preservative treatment could play a vital role in conservation and beneficiation of a diverse and desirable building resource.
The present invention enables creosote to be used as a preservative for lignocellulosic substrates and other substrates in simple and complex formulations, treatments and/or unique wide spectrum or highly specific complementary preservative roles substantially minimising the disadvantages of black, wet, bleeding, staining, tarry, oily, crudding surfaces, skin irritation, odour irritation, flammability, pollution and high energy costs. The potential benefits inherent in a cleaner creosote based preservative/preservation treatment are far reaching and so diverse as the variations in methods of treatment and preservative manipulation immanent in the invention.
Complaints on the handling difficulties associated with high temperature creosote (HTC) treated products were voiced in Australia shortly after the introduction of HTC in 1696. Many poles bled profusely in hot weather and developed tenacious, greasy or viscous tarry glossy surfaces termed "crud". HTC caused tactile skin sensitisation, irritation and burning on many individuals handling the treated timber. Other countries have had similar experience with creosote treated products. Despite extensive work in various parts of the world to elucidate the mechanism of bleeding and crud formation researchers have failed to produce a commercially acceptable improved creosote, and the problem persists.
During the 1970's ultra-fine pigmented HTC emulsions, which were referred to as "pigmented emulsified coloured creosote" and hereinafter termed "pigment emulsified creosote", were being developed in Australia. The emulsions consist of HTC, water and pigment, together with a small amount of emulsifiers and stabilisers. The result was a wood preservative based on creosote which provides a clean, aesthetically pleasing commodity.
Australian Patent No. 514 897 discloses those oil-in-water emulsions of creosote containing pre-dispersed micronised pigments which emulsions were produced under conditions of ultra-high shear. Such emulsions do not have the stability of the compositions of the present invention in the presence of wood extractives. In use under severe conditions of high temperatures and pressures and continuous shear the present compositions are superior to those of 514 897. The compositions of the invention are much less susceptible to contamination than those of 514 897.
Initially the creosote emulsion of 514 897 was used for brush, spray or dip treatment in general domestic applications, such as fencing and outdoor furniture. In 1975 the State Electricity Commission of Victoria (SECV) together with the Commonwealth Scientific and Industrial Research Organisation (CSIRO) tested the early emulsion in a pilot scale pressure treatment of round eucalypt pole stubs. The treated samples when removed from the cylinder were very wet, exhibiting a sludge-like pigment coating. However, the surface emulsion broke quickly upon exposure to air and the stubs dried rapidly.
A further pilot scale trail was then undertaken in which 200 transmission poles were treated with the emulsion of 514 897. The success of this trial not only demonstrated the stability of the emulsion but provided treated poles which were dry an aesthetically pleasing. On the basis of this result a contract was let to treat 3000 full sized eucalypt poles, and this commercial trial was commenced in 1979. In order to produce large volumes of the emulsion of 514 897 for the trial a new emulsion plant was commissioned. Unfortunately the emulsion was contaminated with residual Tanalith C solution remaining in the treatment plant and this led to an unstable emulsion which degraded after fourteen treatments. The emulsion was found to be a coarse dispersion of water/creosote mixture and not an ultra-fine emulsion as originally used. The trial was terminated after less than one third of the proposed poles was treated, because the emulsion could not be re-constituted.
More recent intensive research has led to the development of the present invention which provides a much more stable emulsion. An experiment has been designed to compare and contrast the invention with HTC, in terms of weight retention, penetrability, distribution, exudation, wetness, surface drying, cleanliness and smell.